1. Field of the Invention
This invention relates to apparatus for making window patches from a web of patch material and more particularly to vacuum conveying apparatus for advancing a web of patch material with adhesive on selected portions of one surface thereof along a linear path a preselected distance to severing apparatus for severing successive window patches for application around the periphery of the windows formed in envelope blanks or an envelope web and to a web positioning device for positioning the web in the severing apparatus to prevent contact between the severing apparatus and the adhesive.
2. Description of the Prior Art
The severing of patch material from a web and positioning patch material in overlying relation with the window portion of an envelope blank or a web of envelope material is disclosed in U.S. Pat. Nos. 3,869,965; 3,745,893; 3,618,483; 3,431,830; and 3,410,162. The adhesive material can be applied to the periphery of the window portion of the envelope blank and then the severed window patches applied to the envelope blank with the adhesive thereon, such as disclosed in the U.S. Pat. No. 3,869,965. In the alternative, as disclosed in the U.S. Pat. No. 3,618,483, a patch severing apparatus is arranged to sever window patches of selected length. The window patch web is transferred to the periphery of a vacuum roll. A knife blade positioned on the periphery of a vacuum roll cooperates with an adjacent backing knife blade to sever a window patch from the web after the web has been transferred to the vacuum roll. Adhesive is then applied to the severed patch after it is released from the vacuum roll. In the U.S. Pat. Nos. 3,410,162 and 3,745,893 adhesive is applied to the web of window patch material before the web is severed. The web with adhesive applied thereto is transferred to a vacuum roll. The web is then cut on the vacuum roll by the knife of a rotating cutter roll to form individual patches that adhere to the periphery of the vacuum roll. The pregummed patches are then applied to the envelope blanks or envelope web. In U.S. Pat. No. 3,410,162 the vacuum roll is covered with a porous screen or fabric to distribute the partial vacuum from the ports of the roll over a large portion of the surface of the vacuum roll.
After the adhesive material is applied to the web of window patch material or to the severed window patch, it is preferred that the adhesive be permitted to preset prior to application to the envelope blank or web of envelope material. Presetting of the adhesive assures positive bonding between the window patch and the envelope blank or web. If the vacuum roll is positioned closely adjacent to the adhesive applicator, there may be insufficient time for the adhesive to preset before the web is severed and the patch applied to the envelope blanks, particularly for a high-speed patching operation.
Therefore, there is need in high-speed window patch making operations for patch severing and applying apparatus that assures positive bonding of the window patch to the envelope blank to eliminate incomplete bonding of the patch to the envelope blank by permitting a desired presetting of the adhesive before the patch is applied.
Further, if one employs patch severing apparatus independent of a vacuum roll to allow only severed window patches with adhesive thereon to be provided to the vacuum roll, there is a possibility that some of the adhesive on the web could come in contact with the patch severing apparatus and interfere with its operation. Accordingly, there is a need in such a high-speed patching operation to insure that there is no contact between the adhesive and the severing apparatus.